C :: Free Not Working After Malloc Was Used To Allocate Memory
Jun 13, 2014
Consider this program:
Code:
// sb_string class v1.04
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct sb_string {
[Code] ....
And here is the output I got:
Code:
[harshvardhan@hari-rudra] ~/Desktop% gcc49 -o test test.c
[harshvardhan@hari-rudra] ~/Desktop% ./test
-before Value of len = 1
(in_function)-before Value of len = 1
(in_function)-after Value of len = 1
-after Value of len = 1 I was trying to make a little easier to work with string. Once the memory is allocated by malloc via sb_init() function, the sb_massacre function wasn't working to deallocate the memory. I had used multiple versions of gcc and clang but the result is same.
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Nov 5, 2014
There is a part in the lesson that explains how malloc is used to allocate free memory to a pointer and gives us 2 examples:
Code:
float *ptr = malloc( sizeof(*ptr) ); and Code: float *ptr;
ptr = malloc( sizeof(*ptr) );
From my logic in the first case we allocate the memory to *ptr and in the second to ptr.
It's a bit confusing, am I missing something?
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May 11, 2012
I have a question about the KLU library for LU factorization of sparse matrices. The KLU library accepts a pointer to a memory allocator function, by default it is malloc(). Then it uses this pointer to allocate the memory required.
I want to extend the library and I now have object of classes. I want to use the operator new instead of malloc to allocate the memory. In the same time I want the new operator to call the constructors of the objects. Is there a way to do it?
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Apr 17, 2014
My application calls malloc in multiple subroutines, finally releasing all using free. This is done using my zalloc library (see my other post: [URL] .....
Somehow, when the applications tries to detect the available ammount of memory at the end of the test (allocating, freeing, testing), the freemem function gives me about 4-6MB less memory than at the start of the test? (out of 21MB available on the device at the start).
All memory is allocated and freed using the malloc/free routines within the library, with the exception of the SDL functions, which are registered externally on allocation and release.
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Apr 6, 2014
This program works as expected:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
unsigned long long int address;
float current;
unsigned char pressure_units;
}
[code]....
But I don't like how I had to use malloc and free. Is there a different way to accomplish copying the string into a char pointer without resorting to dynamic memory allocation?
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Dec 22, 2012
Goal: To allocate some memory as a char*, read in some binary data, re-interpret it as a float* and then free the memory.
My code looks like:
void someFunction(float* &result) {
char * tmp = new char[1000];
//...Fill the char buffer here...
result = (float*)tmp; //Reinterpret binary data as floats
[Code] ....
Is the cast back to char* necessary on the red line (or could I have validly left it as float*)? Would it be different if I had written char * tmp = (char*)malloc(sizeof(char)*1000); on the blue line (and correspondingly used free (char*)floatData on the red line?
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Oct 25, 2013
I'm currently learning templates -- & my logic is in a knot with what I am trying to do which is the following:
-Create a function name load
-Accepts a filename (the filename is a text file of integers)
-Open the file
-Create an array(dynamically allocating an array) filling it with the elements read in from the file & returns the array(so that the return type of the array is a pointer to the element type of the array).
//Header file:
#ifndef BUBBLE_SORT_H
#define BUBBLE_SORT_H
#include <iostream>
template <typename T>
void load(std::string filename, T *&arr, int *size);
[code].....
how to allocate memory when it comes to using templates..
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Nov 8, 2013
I am trying to make a function that allows me to allocate memory to a "mem" variable and setting each of its chunk's status to FREE. FREE is defined as 0. Below is my code of the function.
Code:
int allocate(mem *mm, int num_chunks, int chunk_size) {
int i;
mem *temp;
if((mm = (mem *) malloc((num_chunks + 1) * chunk_size)) == NULL){
perror("Failed to Malloc
[code]...
mem; If my function works the way it should, it should print out five 0 because that is how I set them in the function, but this is not the case. I've looked at my function for 2 hours, but I could not figure out any logical error. Now, I think my problem lies with my limited knowledge of pointer arithmetic. On the other hand, when I insert 1000 as the second argument into my function, it gives seg faults, which is not the case for smaller values like 5, 10, 15, etc.
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Jan 13, 2013
what i want to do is if memory allocation fails it display a message shown in the example but its not working
vehiptr = new VEHICLE[vnum];
if(vehiptr == 0)
{
cout<<"Failed to Allocate Memory"<<endl;
return main();
}
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Mar 8, 2014
I’m writing an application for raw image processing but I cannot allocate the necessary block of memory, the following simple code gives me an allocation error.
double (*test)[4];
int block = 32747520;
test = new double[block][4];
off course with smaller block size (i.e. int block = 327475;) it works fine. Is there an allocation limit? How it is possible to deal with big blocks of memory?
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Sep 24, 2014
I CANT use std::string, classes, constructors for this project. I am required to use this archaic method of c-style strings with dynamic memory allocation occurring outside the struct.. i know its not the best way to go about this, but there's nothing i can go. I have a struct:
struct card {
char *suit;
char *rank;
int cvalue;
}
I've created a pointer of size 52 for my deck
card *deckPtr = new card[52];
card *deckHome = &deckPtr[0];
I then try to use
for(int i=0;i<52;i++) {
(*deckPtr).suit = new char[8];
(*deckPtr).rank = new char[7];
deckPtr++
}
deckPtr=deckHome;
I am essentially trying to fill in these arrays from a card file, but I cannot make it past running the program, i get sa seg fault which I dont understand why.
I dynamically allocate memory in my card read in function..
void cardInit(card *deckPtr) {
card *deckHome = &deckPointer[0];
ifstream fin;
char *finName = new char[13];
cin >> *finName
fin.open(finName)
[Code] ....
Its a pretty simple program..and my dynamic memory works for the file name, but I cant figure out why it doesnt work for structs?
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Jan 8, 2014
This compiles o.k.:
Code:
int main(void){
char *a;
a = (char*) malloc (100*sizeof(char));
[Code]....
I get an error saying "pointer being freed was not allocated". This happens for free(a), free(*a), free(&a), free(&*a).
So if I no longer need "1234567"... how do I get rid of this memory element?
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Mar 16, 2014
I'm trying to free allocated memory for structure. It seems like free() gets only pointer and not regular types . my question is basic and simple – is passing pointer to free() frees the pointer or the variable it points at? or both?
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Aug 30, 2013
So my assignment is to create a program that calls for a function in main that dynamically allocates an array[3] and then have pointers with multiple levels of indirection and pass them by reference so they are not lost after the function. Here is my code:
#include <iostream>
#include <array>
#include <iomanip>
#include <string>
[Code]....
Next part is to ask user for two non-negative numbers and then get the length of those numbers and create an array. for the size of each number they input. Then to separate those numbers and add the cross-sums.
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Jan 2, 2013
A special hardware unit with some storage in it is connected to your computer and is memory-mapped so that its storage is accessible in the address range 0x55500000 – 0x555fffff. You want to interface this hardware unit to your C++ program so that dynamic memory is allocated in this hardware unit, not in your computer’s memory. Implement a class MyHardwareMemAllocator which has the following function.
void * allocMemoryInMyHardware(int numberOfBytesToAllocate);
which returns a pointer to the allocated memory chunk, or null if unable to allocate.
C library calls like malloc are not allowed.
1) How to allocate memory from given address range.
2) How to check whether this required memory space is available or not for allocating
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Apr 9, 2012
I use the array of Radiobutton,string,.. in my project. How i can destruct these array from memory,because i see the stackoverflew exception.
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Jan 24, 2013
I created a structure containing two variables of type char.
i.e. char name[64],char details[128];
And a pointer to structure now when I write this name and details to file and now I want to change the particular name.
i.e. To modify then if the stored file name is greater than the entered name then it is erasing the next record line also I need to allocate some memory.
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Nov 22, 2013
How to free the memory and address,value
Server:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
[Code] .....
Client:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
[Code] .....
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Feb 25, 2015
An attempt to create a class which is basically a mimic of vector<int> i don't seem to know how to delete pointer x in a destructor to free memory, also on pushback and pushfront methods, i can't free y when i implement delete[] y; y=NULL; i get some NULL out put when cout 'ing the object in main, why is that happening and how do i free memory y.
#include<iostream>
using namespace std;
class vectorOfint{
int* x;
int size;
public:
vectorOfint();
[Code] .....
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Oct 17, 2014
Code:
int *p, ar[100];
p = (int *)malloc(sizeof ar);
.. *p is a pointer variable, but what means another * here --> (int *)?
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Feb 26, 2013
Having some frustrating issues trying to free memory from a dynamically allocated array of pointers to linked lists. I think the problem is in how I initialize the pointers to NULL. Is there a more elegant way to have the program recognize that the list is empty so it knows to create a head node for the linked list in the function 'add_end_stub_to_array'?
I ran the code through Valgrind and it says that memory is definitely lost from this array.
This is the structure definition.
Code: struct stub_edge {
int loc_id;
int anim_type;
int mkt;
struct stub_edge *next_node;
};
Here is the code snippet from main allocating and deallocating memory to the array.
Code:
struct stub_edge **stub_list = (struct stub_edge **)malloc( sizeof(struct stub_edge *) * 12);
for (i = 0; i < 12; i++)
{
stub_list[i] = (struct stub_edge *)malloc(sizeof(struct stub_edge));
stub_list[i] = NULL;
}
stub_list = add_end_stub_to_array(end_stubs, stub_list);
destroy_end_stub_array(stub_list);
Here the function for adding nodes to the lists by reading through a dynamically allocated 2D array. (The end_stubs array is ordered by month and each linked list represents events occuring within the month).
Code:
struct stub_edge **add_end_stub_to_array(int **end_stubs, struct stub_edge **list)
{
long int i = 0;
int mon = 0;
struct stub_edge *current_node1;
struct stub_edge *new_node1;
int break1 = 0;
while(i < num_edges && break1 == 0 && mon < 12)
[Code]...
Here is the function for freeing memory from the list.
Code:
void destroy_end_stub_array(struct stub_edge **list)
{
if(list != NULL)
{
int mon = 0;
struct stub_edge *current_node1;
struct stub_edge *new_node1;
for(mon = 0; mon < 12; mon++)
[Code]...
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Dec 1, 2014
I am writing a very basic database in C++ and I am accessing the data from a web browser. I am using the opensource Mongoose web server code....
I have an issue...
The way the DB works is this: on starting, the DB loads a json file of all of the data into it. I have a class called DatabaseLoader that does this - it is the class that gets rewritten depending on the data structure of the json.
This is passed to vectors (vector<Node*> and vector<Edge*>) as references from Graph object.
Once the DatabaseLoader has finished it can be destroyed and any memory allocated objects it created (except the ones in those two vectors).
From then on, the Graph object is in charge of all of the elements in the database that are stored in the two vectors. When the user browses to htpp://127.0.0.1:8000 they see the json representing each object in the vectors.
All good so far....
However, when I repeatedly hit refresh in my browser (and call me insane...) at quite a fast speed I get this error:
Code:
main(29855,0x7fff76763310) malloc: *** error for object 0x7f98b2829408: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug
[1] 29855 abort ./main testing.json
It seems to me this would be if I tried to "delete" and object twice, or if one of my objects was overwriting memory somewhere. However I am not recreating anything, I am just looping over the vectors and printing out the content. When I refresh slowly, I dont see this happen - i did it quite a lot of times, but when I do it fast I think it is happening.
So is there any possibility of me hitting the c++ web server to quickly and it is trying to process the data twice, causing some sort of memory error - i.e do I need to implement threading or something??
I can paste code, but there is quite a lot now....
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May 16, 2014
does memory reserved by malloc() get freed when the function it is called in finishes?
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Sep 7, 2013
How can I view the number of bytes that have been allocated by using the malloc function?I tried:
mem = (float*)malloc(num*sizeof(float));
printf("The amount of memory allocated using malloc is %d.", mem);
Note: The variable "num" in my program is equal to 7.But every time I run the program, this value changes.
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Mar 10, 2014
What is wrong with my function why does it spit out huge numbers? And how do i use malloc or calloc to create an array in dynamic memory, and return a pointer to this array
Code:
#include <stdio.h>#include <stdlib.h>
int fibonacci(int n)
{
int i;
long int fib[40];
fib[0]=0;
fib[1]=1;
for(i=2;i<n;i++){
fib[i] = fib[i-1] + fib[i-2];
[Code]....
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Jul 23, 2012
When does malloc() return null ? I want to allocate a big virtual memory which can not possibly fit on RAM, so most of it will be stored on disk. I am going to access the data sequentially so at any one time the data I am working on will fit in RAM. So I am hoping the OS will move the required pages in and out of disk. I can achieve this behavior manually by allocating the required blocks on RAM but this is rather tedious. Say I have an array a[100][10000000000]. At any one time I am working only on a[i-1][], a[i][], a[i+1][] which can fit in RAM but not the whole array. So how do I allocate the array so that I can work on it using for loops for(i=0;i<100;i++) without handling the page movements myself?
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